On 1/7/19 3:53 PM, Benjamin Gilbert wrote: > On Mon, Jan 07, 2019 at 02:03:15PM -0600, Wei Huang wrote: >> On 1/7/19 2:25 AM, Kirill A. Shutemov wrote: >>> On Fri, Jan 04, 2019 at 05:44:11AM +0000, Wei Huang wrote: >>>> In some old AMD KVM implementation, guest's EFER.LME bit is cleared by KVM >>>> when the hypervsior detects guest sets CR0.PG to 0. This causes guest OS >>>> to reboot when it tries to return from 32-bit trampoline code because CPU >>>> is in incorrect state: CR4.PAE=1, CR0.PG=1, CS.L=1, but EFER.LME=0. >>>> As a precaution, this patch sets EFER.LME=1 as part of long mode >>>> activation procedure. This extra step won't cause any harm when Linux is >>>> booting on bare-metal machine. >>>> >>>> Signed-off-by: Wei Huang <wei@xxxxxxxxxx> >>> >>> Thanks for tracking this down. >> >> BTW I think this patch _might_ be related the recent reboot issue >> reported in https://lkml.org/lkml/2018/7/1/836 since the symptoms are >> exactly the same. > > The problem in that case turned out to be https://lkml.org/lkml/2018/7/4/723 > which was fixed by d503ac531a. OK, then it is a different problem. For this specific patch, without it, the latest kernel can't boot on RHEL6 (and other old KVM distros) as a guest VM on AMD box. > > --Benjamin Gilbert >
